The present invention relates to a film prepared from a composition comprising a polyvinyl alcohol and a starch or a crosslinking agent in addition to the above two components, and more particularly to a polyvinyl alcohol-starch film having an excellent water resistance and easily degradable due to mechanical actions or microorganisms living in the soil.
A composition comprising a polyvinyl alcohol and a starch has been widely used in various field. For instance, the composition is used as adhesives, sizing agents for fibers or textiles, or formed into molded articles such as films or sheets, and the like. As to such conventional uses, there are many cases that the property of being capable of solubilizing in water is one character of the polyvinyl alcohol and the starch which is utilized. That is, the character, the solubility in water is effectively utilized in the respects of, for instance, the desizing after sizing warps when using the composition as the sizing agent, the possibility that the film is thrown away into a flush toilet, such as films for sanitary napkin when using the composition as the film, and the like.
However, when above-mentioned polyvinyl alcohol-starch film (the film prepared from the composition comprising the polyvinyl alcohol and the starch) is used as materials suitable for agricultural uses, for instance, films for protecting a root which is suitable for use of protecting a root when transporting or transplanting plants, films (multifilm) for removing weeds which is suitable for use of preventing the propagation of weeds by covering the surface of cultivated fields with the film to intercept the sunlight, tapes for binding into sheaves which is suitable for use of binding rice, barley or wheat plants into sheaves after reaping them, and the like, the poor water resistance of the polyvinyl alcohol-starch film limits the increase of its use.
On the other hand, it has been reported that the polyvinyl alcohol-starch film is decomposed by microorganisms in the soil. Accordingly, if the polyvinyl alcohol-starch film can be used as the materials suitable for agricultural uses as mentioned above, the environmental pollution is not caused, that is, it can be said that such a film is industrially remarkably useful.
When using the polyvinyl alcohol-starch film in the field requiring the water resistance, e.g., as the materials suitable for agricultural uses, the film is forced to be given the water resistance by a hydrophobic resin, for instance, a solution of a vinylidene chloride polymer is coated on the film surface or an other film such as polyethylene film is laminated on the film, and the like.
An object of the present invention is to provide a polyvinyl alcohol-starch film having excellent water resistance and easily degradable due to mechanical actions or microorganisms in the soil.
A further object of the present invention is to provide a use of the above-mentioned film as a material suitable for agricultural uses.
These and other objects of the present invention will become apparent from the description hereinafter.